The present invention relates to a high-density reproducible magnetic recording medium which records and reproduces information magnetically with heating, and a magnetic reproducing method thereof.
Recently, there has been an increasing need for a memory device with a larger capacity to process multimedia information in a broad bandwidth. Among of all, high-density recording and reproducing techniques have been developed actively with rewritable optical disks, magnetic disks, and magnetic tapes.
One of the proposed techniques realizes high-density recording and reproduction by narrowing a track during the magnetic recording and reproduction by means of assist irradiation of light (which is referred to as light assist type magnetic recording and reproducing method, hereinafter).
Incidentally, one of the problems in realizing the high-density recording and reproduction is how crosstalk from a recording bit (hereinafter, referred to as adjacent bit) adjacent to a reproducing bit should be suppressed.
Accordingly, a light assist type magnetic recording and reproducing method which can reduce crosstalk from the adjacent bit is disclosed, for example, in Japanese Patent No. 2617025 issued on Jun. 4, 1997 (corresponding to Japanese Laid-open Patent Application No. 176034/1992 (Japanese Official Gazette, Tokukaihei No. 4-176034, published on Jun. 23, 1992)), which is referred to as the first light assist type magnetic recording and reproducing method, hereinafter. Another light assist type magnetic recording and reproducing method which can also reduce crosstalk from the adjacent bit is disclosed, for example, in Japanese Patent No. 2636957 issued on Aug. 6, 1997 (corresponding to Japanese Laid-open Patent Application No. 95201/1992 (Japanese Official Gazette, Tokukaihei No. 4-95201, published on Mar. 27, 1992), which is referred to as the second light assist type magnetic recording and reproducing method, hereinafter.
In the first light assist type magnetic recording and reproducing method, a ferrimagnetic material having a magnetic compensation temperature around room temperature is used as the recording medium. Here, information is recorded in the following manner: a light beam is irradiated to the recording medium along a target recording track to raise a temperature thereof around the curie temperature, and then an external magnetic field is applied to the target track by a recording magnetic head. Also, the information is reproduced in the following manner: a target reproducing track is irradiated by a light beam to raise a temperature thereof so as to increase magnetization in a target reproducing portion, and then a magnetic flux leaking therefrom is magnetically reproduced into information by a magnetic reproducing head.
According to the first light assist type magnetic recording and reproducing method, areas other than the reproducing portion are heated to the magnetic compensation temperature. Thus, the leaking magnetic flux is so small that crosstalk from a track adjacent to the target reproducing track, that is, crosstalk from the adjacent bit, can be reduced.
In the second light assist type magnetic recording and reproducing method, the information is reproduced in the following manner: a light beam is irradiated to a track adjacent to the target reproducing track so as to raise the temperature thereof around the magnetic compensation temperature. Consequently, an adverse effect of the leaking magnetic flux from the track adjacent to the reproducing track is suppressed, and therefore, crosstalk from the same, that is, crosstalk from the adjacent bit, can be reduced.
Incidentally, in order to suppress crosstalk from the adjacent bit during the high-density recording and reproduction, both the first and second light assist type magnetic recording and reproducing methods use ferrimagnetic materials having the magnetic compensation temperature as the recording media.
However, because the ferrimagnetic material has temperature characteristics that the magnetization varies sharply around the magnetic compensation temperature, each of the first and second light assist type magnetic recording and reproducing methods has the following problems.
That is, in the first light assist type magnetic recording and reproducing method, if room temperature varies during reproduction, corresponding non-zero residual magnetization is induced from the track adjacent to the target reproducing track. In the second light assist type magnetic recording and reproducing method, corresponding non-zero residual magnetization is induced from the track adjacent to the target reproducing track if the heating temperature varies during reproduction.
Consequently, a leaking magnetic flux is caused as crosstalk by the residual magnetization induced from the track adjacent to the target reproducing track, and overlaps with a reproducing signal, thereby deteriorating the S/N of the reproducing signal.
It is therefore an object of the present invention to provide a high-density reproducible magnetic recording medium, from which a reproducing signal with excellent S/N is obtained, and a magnetic reproducing method thereof.
In order to fulfill the above and other objects, the magnetic recording medium of the present invention is characterized in that it has a magnetic layer which records a magnetization direction in accordance with information, and that the magnetic layer includes two magnetic films having the same magnetization directions in a reproducing area and opposite magnetization directions in the other areas.
According to the above arrangement, information is reproduced from the reproducing area in the magnetic layer of the magnetic recording medium.
Incidentally, in a conventional magnetic recording medium including a ferrimagnetic material having a magnetic layer of a single-layer structure, magnetization in an area (adjacent area) adjacent to the reproducing area in the magnetic layer is eliminated by keeping the adjacent area at the magnetic compensation temperature. Consequently, crosstalk caused by the magnetization in the adjacent area can be prevented, so that a reproducing signal obtained from the reproducing area is not adversely affected.
However, the magnetization of the ferrimagnetic material varies sharply depending on temperatures around the magnetic compensation temperature. Thus, only a slight shift from the magnetic compensation temperature in the adjacent area makes elimination of the magnetization impossible, thereby producing non-zero residual magnetization therein.
In contrast, according to the arrangement of the present invention, the magnetic layer includes two magnetic films, and the magnetization directions of these magnetic films are the same in the reproducing area and opposite in the other areas. Consequently, the magnetization of each magnetic film is intensified by the other in the reproducing area and cancelled out by the other in the other areas.
In other words, even if the temperature changes in the areas other than the reproducing area, the residual magnetization induced in each magnetic film is cancelled out, because the magnetization directions are opposite. Thus, crosstalk caused by the residual magnetization induced by a temperature change can be prevented in a reliable manner. On the other hand, because the magnetization directions of the two magnetic films are the same in the reproducing area, a total of the magnetization of each magnetic film becomes large, and so does a reproducing signal.
As has been discussed, according to the present magnetic recording medium, crosstalk can be prevented in a reliable manner, thereby realizing the recording at a higher density.
Also, in order to fulfill the above and other objects, the magnetic reproducing method of the present invention is a reproducing method for a magnetic recording medium having a magnetic layer including two magnetic films, characterized by having the steps of:
(a) aligning the magnetization directions of the two magnetic films in the reproducing area in the same direction; and
(b) aligning the magnetization directions of the two magnetic films in areas other than reproducing area in opposite directions.
According to the above method, the magnetization directions of the two magnetic films are aligned in the same direction in the reproducing area and in the opposite directions in the other areas. Consequently, the magnetization of each magnetic film is intensified by the other in the reproducing area, and in the other areas, even if the residual magnetization is induced by a temperature change, the residual magnetization of each magnetic film is cancelled out by the other.
Hence, not only can a large reproducing signal be obtained from the reproducing area, but also crosstalk caused by the residual magnetization in the other areas can be prevented in a reliable manner, thereby realizing the recording at a higher density.
For a fuller understanding of the nature and advantages of the invention, reference should be made to the ensuing detailed description taken in conjunction with the accompanying drawings.